*{
  margin: 0;
  padding: 0;
  list-style: none;
}
.box{
  width: 500px;
  height: 300px;
  margin: 50px auto;
  overflow: hidden;
  border:1px solid #333;
  position:relative
}
.banner_box{
  width:2000px;
  position: relative;
  height:100%;
  overflow: hidden;
  li{
    float: left;
    width:500px;
    height: 300px;
    overflow: hidden;
    line-height: 300px;
    font-size: 100px;
    text-align: center;
  }
}
.arrow_box{
  position: absolute;
  z-index: 10;
  width: 100%;
  height: 100%;
  top:0;
  left: 0;
  span{
    width: 30px;
    height: 50px;
    top:50%;
    margin-top: -25px;
    background: #333;
    color:#fff;
    position: absolute;
    cursor: pointer;
  }
  .right{
    right: 0;
  }
}